Add Release notes

[tOverney]

Hi @tototoshi !
It's awesome that we're getting new versions of scala-csv, thank you very much for it 🥳

Would it be possible to start adding releases notes on the releases at https://github.com/tototoshi/scala-csv/releases
or add a CHANGELOG.md on the repo?

Right now discoverability of the changes when updating to the new version is not ideal
(e.g. this breaking change is very easy to migrate but not really documented :) )

Thank you in advance!